Yaws

Key facts

Yaws is a neglected tropical disease that affects the skin, bone and cartilage.

The disease is caused by a bacterium from the same group of organisms that cause venereal syphilis; however, the transmission of yaws is not sexually-related.

Yaws can be eradicated as humans are the only reservoir.

A recent finding has shown that that a single, oral dose of the antibiotic azithromycin can completely cure yaws, opening up prospects for large-scale treatment of affected populations.

2 countries - Ecuador and India - which were once endemic reported interruption of transmission in 2003.

12 currently endemic countries need support to implement WHO’s new eradication strategy.

Yaws forms part of a group of chronic bacterial infections caused by treponemes which include endemic syphilis (bejel) and pinta and are commonly known as endemic treponematoses. Yaws is the most common of these infections.

The disease is found primarily in poor communities in warm, humid and tropical forest areas of Africa, Asia, Latin America and the Pacific.

Yaws is also known as framboesia (German or Dutch) and pian (French) and affects the skin, bone and cartilage. It is caused by T. pallidum subspecies pertenue. This organism belongs to the same group of bacteria that cause venereal syphilis.

Yaws is transmitted through direct (person-to-person) non-sexual contact with the fluid from the lesion of an infected person. Most lesions occur on the limbs. The initial lesion of yaws is teemed with the bacteria. Contact with this fluid, especially among children who play together and sustain minor injuries, leads to transmission of infection. The incubation period is 9–90 days (average 21 days).

About 75% of people affected are children under 15 years old (peak incidence occurs in children aged 6–10 years). Males and females are equally affected.

Overcrowding and poor socio-economic conditions facilitate the spread of the yaws. Without treatment, infection can lead to chronic disfigurement and disability.

Scope of the problem

The eradication campaigns of 1952-1964 targeted 46 countries. Since 1990, formal reporting of yaws to WHO stopped due to the discontinuation of yaws eradication programmes in many countries. Only a few countries kept yaws as part of their public health agenda.

A review of historic documents from the 1950s shows that at least 85 countries within the tropical belt 20 degrees north and south of the equator, were endemic for yaws. However, only 12 are known to be currently endemic for yaws, while 2 countries, Ecuador and India, which claim to have interrupted transmission in 2003, need to be verified. Furthermore, WHO also plans to assess the status of yaws in 71 previously endemic countries.

Reporting of yaws is not mandatory so the available data, published in a recent edition of the Weekly Epidemiological Record are only indications of the global distribution of the disease.

Surveys are currently in progress to assess the full extent of the disease. The current status of yaws in countries of 4 of the 6
regions of WHO is as follows:

Yaws: status of endemicity (known and unknown) in 4 out of 6 WHO regions in 2012

Diagnosis

Clinical

There are two basic stages of yaws: early (infectious) and late (non-infectious).

In early yaws, an initial papilloma (a circular, solid, swelling on the skin, with no visible fluid) develops at the site of entry of the bacterium. This papilloma is full of the organisms and may persist for 3–6 months followed by natural healing. Bone pain and bone lesions may also occur in the early stage.

Late yaws appears after five years of the initial infection and is characterized by disfigurement of the nose and bones, and thickening and cracking of the palms of the hand and the soles of the feet. These complications on the soles of the feet make it difficult for patients to walk.

In the field, diagnosis is primarily based on clinical and epidemiological findings. WHO has recently published a clinical pictorial guide to help health and community health workers identify the disease.

Serology

Serological tests are widely used to diagnose treponemal infections (e.g. syphilis and yaws).

Rapid tests however cannot distinguish between active yaws and treated infections. New rapid dual non-treponemal and treponemal point-of-care syphilis tests hold promise for rapid confirmation of active yaws in the field. Studies are in progress in Ghana, Papua New Guinea, Solomon Islands and Vanuatu to evaluate this new test.

PCR

Genomic analysis using polymerase chain reaction (PCR) can be used to definitely confirm yaws. The PCR technique can also be used to determine azithromycin resistance from swabs taken from yaws lesions.

Complications

Without treatment, about 10% of affected people develop disfiguring and disabling complications – deformities of the legs and nose - after five years. The disease and its complications cause school absenteeism and prevent adults from farming activities.

Prevention

There is no vaccine for yaws. Prevention is based on the interruption of transmission through early diagnosis and treatment of individual cases and mass or targeted treatment of affected populations or communities. Health education and improvement in personal hygiene are essential components of prevention.

Past eradication efforts

Between 1952 and 1964, WHO and UNICEF provided assistance to 46 countries with the aim of eradicating endemic treponematoses. Mass campaigns in these countries examined over 300 million people and treated 50 million.

By 1964, the prevalence of these diseases had decreased by 95% (2.5 million). This achievement is considered to be one of the success stories in public health but this was not sustained until the end goal – eradication. However, premature integration of yaws control activities into the weak primary health-care systems and lack of continued surveillance were partly responsible for the world’s inability to eradicate yaws. Resurgence in the 1970s prompted a World Health Assembly Resolution WHA 31.58.

Renewed eradication efforts: progress so far

The “WHO Roadmap for NTDs” and WHA resolution 66.12 have set 2020 for the eradication of yaws from the remaining endemic countries.

Since January 2012, when the “WHO Roadmap for NTDs” and an article in the Lancet on the efficacy of a single-dose azithromycin in the treatment of yaws were published, WHO has taken steps to move the renewed eradication efforts forward:

In March 2012, WHO convened a meeting of experts to develop a new eradication strategy and policy based on a single-dose treatment with azithromycin. These are:

Total Community Treatment (TCT) – treatment of the endemic community, irrespective of the number of active clinical cases.

Total Targeted Treatment (TTT) – treatment of all active clinical cases and their contacts (household, school and playmates).

In March 2013, WHO convened another meeting to develop criteria and procedures for the verification of interruption of transmission and a guide for programme managers.

As a first step in implementing the new eradication strategy as a proof of principle, 7 countries were selected for the initial pilot treatment campaigns.

In 2012, MSF implemented the first treatment Bétou and Enyellé districts of Congo.

In 2013, implementation was carried out in Ghana (West Akyem district), Papua New Guinea (Lihir island) and Vanuatu (Tafea Province) achieving a coverage of more than 90%.

LSHTM is providing technical and serological support for surveys in Solomon Islands; and

Noguchi Memorial Institute for Medical research, Accra Ghana, Papua New Guinea Institute of Medical Research and other national laboratories are participating in the evaluation of rapid dual non-treponemal and treponemal POC Syphilis test and azithromycin resistance testing.

Perspective

Yaws is eradicable as humans are the only reservoir. Covering all at-risk populations through large scale treatment programmes with oral azithromycin will interrupt transmission and eliminate the disease in a given area.

The momentum to achieve this is gathering pace and WHO, together with partners, is spearheading renewed efforts to eradicate yaws.

The provision of azithromycin in sufficient quantities, the availability of a rapid diagnostic test and adequate funding are critical to ensure the smooth implementation of activities to reach 2020 target.